1. Field of the Invention
The present invention relates to a catalyst for acrolein oxidation, more particularly, to production of the catalyst containing molybdenum, vanadium, and tungsten as essential components.
2. Description of the Related Technology
In producing of acrylic acid, oxidation reactions of acrolein with oxygen molecules in the presence of a catalyst have been widely used. The preparation of the catalyst has been researched to obtain a high yield of the acrylic acid, which are primarily directed to the components of the catalyst and the composition thereof. Also, some methods of producing a carrier-retained catalyst have been provided in the prior art.
Japanese Patent Application Laid-Open Nos. Showa 49-117419, Showa 58-166939, and Showa 64-63543, and European Patent Application Laid-Open No. 293,859/1988 disclose methods for producing a carrier-retained catalyst, in which aqueous solutions of metallic salts of catalyst components are mixed and coprecipitated to produce a suspension of a catalyst. An inert carrier, which has a small surface area and a large aperture ratio, such as round or cylindrical silicon carbide, silica, and silica-alumina, is added to the suspension, and water is evaporated by heating the suspension with agitation to produce a catalyst retained within the structure of the inert carrier.
Further, in U.S. Pat. Nos. 4,157,987/1976, 4,259,211/1981, and 4,892,856/1990; and Korean Patent Application Laid-Open No. 7409/1993, a suspension of a catalyst is heated to evaporate water while being stirred. Anhydrous solid of the catalyst is obtained and is ground to powder, which is coated on an inert carrier, such as alundrum, by using a coater.
The inert carriers retain the catalyst in their structures and prevent the release of the catalyst at a time. Accordingly, occurrence of excessive oxidation reactions, which may be caused by supply of abundant catalyst, can be avoided. Also, the inert carrier functions as heat buffer by absorbing the heat generated during the oxidation reaction.
Korean Patent Application Laid-Open No. 7409/1993 and U.S. Pat. No. 4,892,856/1990 disclose that physical properties, such as non-surface area, pore volume, and pore diameter distribution, vary in the catalysts prepared even from the identical component metallic salts and composition thereof. The variance in the physical properties of catalysts results in the variance in the catalytic performance of catalysts, i.e., the acrolein turnover ratio and acrolein yield. This means the physical properties and accordingly the catalytic performance of the catalysts change, depending on the preparational manipulations as well as the conditions thereof, which also causes the lack of reproducibility in preparing the catalyst. In addition, these variances of the catalytic performance sometimes exceed those by the changes in the components and the composition of the catalyst.
However, there has not yet been a report, which satisfactorily addresses that the physical properties and accordingly catalytic performance of a catalyst change, depending on the process of producing the catalyst including the preparation of a suspension or powder therefrom.
Meantime, in the preparation of the aqueous solution of metallic salts, an excessive amount of water is required to dissolve some metallic salts having low solubility in water, such as ammonium metavanadate and ammonium paratungstate. The amount of water in the suspension of the catalyst is from about 5 to about 10 times by weight of the salts. The solubility improves when the temperature of water increases, but heating of the aqueous solution of the salts deteriorates the catalytic performance.
The water used to prepare the suspension has to be completely removed to form a powder catalyst. Accordingly, the amount of energy and time required to remove the water has a direct relation to the amount of water used. Further, in the case where an inert carrier is added to the suspension to produce a carrier-retained catalyst, additional time is required to remove the water within the carrier structure.